I hate to hear this, Father, after you have worked so hard to simply keep these plumeria alive.
You may have to resort to a commercial spray, such as Bayer Natria Insect Disease & Mite Control, but in the meantime, simple water can help control them. Wet a soft rag with water and gently wipe all the leaves, top and particularly bottom, with the water. You can add a little dish detergent, but its really not necessary. Rinse and squeeze the rag regularly as you do the wiping. Repeat this every 3-5 days. Also, any leaves that show significant yellowing or damage, get rid of them. At least you don't have a lot of plants to deal with, so wiping won't take much time.